Challenges faced by digital printing
Aslam Khan, Textile Consultant.
The digital printing technology
is advancing rapidly as well as facing new challenges to meet
the market requirements. These can be summarized as follows:
Cost, ease of technology, nozzles, training of personnel, heads
and pigment printing.
The cost of this technique is the main hindrance in the
advancement of this technology because existing techniques
available in the market are a much cheaper option as compare to
digital printing. However, this sector offers a lot of
attraction, especially for the high-end market.
The nearest comparison is the flatbed printing technique,
which offers dyes and chemical cost of Rs.15 per sq/m with
reactive dyes while digital printing ink will cost about Rs. 75
per sq/m. The cost of capital is also very high. However, in
the near future, the cost is going to come down and replaceable
parts become more affordable. This coupled with the speed of the
machine will force the printers to replace even rotary printing
machines. The main consumables contributing to cost in this
technique are the print heads, other than ink cost. So the
development of durable heads, with a long life, is a
prerequisite to reducing cost in the long run.
Ease of technology
In the past five years, the techniques have improved but
still, it has not reached the stage where it can outclass the
conventional techniques available in the market. In the
single-pass technique, grey and solid blotches need
improvements. Heads require new dimensions and hardware
techniques. Pigment printing needs to be addressed in depth as
this will create a revolution in the field of textile printing
as 85% of conventional printing is still performed with
pigments. Pigment inks need to pass through an extensive R&D
cycle. Possibilities could be a development of a block polymer
of polyurethane and acrylate or incorporation of a positive
charge on textiles may improve the adhesion of the pigment.
The nozzles need to be modified specially for pigment
printing as the size of pigments particles is bigger than
dyestuff, therefore they can easily clog nozzles. It is
paramount that the size of the pigment particle must be reduced,
without impairing aesthetic properties. For example, the main
problem faced by reducing the particle size to below 1 micron is
the reduction of colour yield and brilliance of shade. Success
is only thus achievable if pigment chemistry and nozzle
engineering are addressed simultaneously. The auxiliaries, such
as solubilizing agents may play an important part in pigment
inks in time to come.
Training of Personnel
The training regarding repair and maintenance of machines and
hardware is going to play a very vital role in promoting this
technique. To face these challenges, one must have knowledge of
different mechanisms and the parts of the machines.
The digital textiles printers were introduced in the 1980s,
and by early 1990s, the prices become more affordable, thereby
attracting the conventional textile printing market for
commercial printing. Apart from the price there are positive and
negative aspects which can be summarized below:
- The level of flexibility varies from warp to weft.
- Different varieties of synthetic fibres and their
compatibility with various dyes, which gives the problem of
changing inks and also effects the performance of heads.
- Behaviour of stretch fabrics, highly porous and textured
- Fastness properties of the prints.
- The designs need to be developed for the digital format.
- The design and colour management software, inks, fabric
pretreatment, post-treatment and all the operations are
- The lower energy, water, short runs, total elimination
of screens, less space, material consumption, and
environment are positive points.
In case of the digital printer, the liquid ink in various
colours is ejected onto the textile without actually touching,
thereby, printing a high-resolution image. A printhead scans
the fabric in horizontal stripes by moving left to right and
back again while the fabric is rolled up in vertical steps.
The drops that are ejected are a sub-micron size which is
much smaller than the diameter of human hair. One sq. meter of
print may contains over 20 billion droplets; Positioning has to
be very precise to achieve resolutions as fine as 1400x1400 Dots
Per Inch (DPI). The resolutions and number of heads describe the
speed of the machine; this can only be achieved by using the
inks prepared by Nanotechnology.
There are two types of head technologies used when it comes
to ink jet printers. The CIJ continuous inkjet or DOD drop on
In continuous ink jet, the droplets are generated
continuously with an electric charge imparted to them. The
charged droplets are ejected from a nozzle.
The charged droplets are either directed to the textile for
printing or they are directed to a recycling system. Since the
droplets are generated continuously they are directed to the
textile only when and where a dot is desired. The Hertz CIJ was
the basis of the first commercially available digital textile
printing system introduced by Stork (Now SPGPrints) in 1991
using Osiris “Iris’’ printhead technology. In DOD system the ink
is ejected from the printhead only when needed.
In DOD the heads are driven by Piezoelectric system PIJ,
where the ink is forced from the print head by a Piezoelectric
actuator by a squeezing mechanism, or by a thermal mechanism. In
this system, an electric heater inside each nozzle is used to
rapidly increase the temperature of the ink which causes a
vapour bubble to expand and allow for ejection of an ink
Ink jet printer heads and their
The most common inkjet printers head used in the present
popular digital textile printing machines are as follow:
- Epson DX5 (Mutoh RJ900, Mimaki JV33, Mimaki JV5).
- Epson DX7 (Mutoh 1683, Roland XF. 640).
- Seiko 508 GS (FlexJS- BT-180, Ichinose 2030).
- Ricoh Gen. 4 (d.gen Telieios Grande, Mimaki TX 400).
- Ricoh Gen 5 (Mimaki TX 500).
- Konica KM512 (Konica Minolta Nassenger vii).
- Kyocera Kj4B (MS JP6, MS LaRIO, EFI Reggiani ReNoir).
- Precision Core (MEMS) Technology.
- Fuji Samba (MEMS).
- Zaar 5501.
The difference in the print head technology comes from the
configuration of different Print head such as:
Print head width: The width of Print head
varies from 25 mm to 108 mm. A large print head increases the
speed of the machine by displacing more fabric on each scan of
print carriage. Also speed can be enhanced by increasing the
number of PH’s.
Channels and Nozzles: The Print head has
different configuration of channel to accommodate different
inks. Each channel has specific nozzles which affects the
printing resolution as nozzle density can be as high as 2048 per
43mm PH as in the Fuji Print Heads deployed by SPGPrints.
Frequency (KHz): The number of drops per
seconds, directly impacts printing speed.
Minimum drop size (Picolitre): The print heads are capable of
producing variable drop sizes, small drop size provide finer
details at the expense of printing speed.
Binary versus greyscale
The size of individual ink drops directly affects overall
output quality. In general, small drops produce good definition
and higher resolution and suited for textiles’ while large drops
cover large areas quickly and are good for printing large flat
areas. Many printers take the binary approach with every drop
being the same size because it is faster.
The alternative is to vary the size of ink drops, a technique
is usually known as grey scale printing. There are a number of
advantages to this such as mixing smaller and bigger drops make
it easier to deal with gradients and slight tonal shifts. In
addition to softer tonal gradients, fuel consumption has also
economized because small droplets give a higher print coverage,
and reduce dithering.
There are three basic approaches. The first one is actually
firing different size by varying the electrical power used to
generate the drops.
Secondly, one can fire a very heavy drop of ink, which will
stretch out as it flies through the air and break apart into
larger and smaller droplets.
Third and the latest alternative is known as multipulsing and
involves quickly firing two drops of ink that then merge into a
single larger drop, usually in flight before they hit the
Mostly print heads use a combination approach. To calculate
the print head productivity we can apply the Ross Allen of
Hewlett Packard equation. Where,
A= Area fills rate. (inches per second)
F= Drop rates. (Hertz )
R= Print resolutions. (dpi)
However it indicates the problem of resolution if you double
the resolutions from 360 to 720 and keep the frequency and
number of the nozzles same, the productivity reduces by a factor
The mechanism of printing depends on two principles,
multi-pass or scanning and single-pass Scanning.
Multiple pass: In multi-pass or scanning the fabric is held
stationary as the carriage traverses across the width of the
fabric, and once it reaches back to its starting position, the
fabric moves forward one step.
Single pass: In a single pass, print heads are mounted over
the full width of the fabric, one bar of stacked print head per
colour, fabric moves with constant speed under these bars. The
image is built upon vertical lines.
MS Lario is the commercial example of this system, Pike of
SPGPrints, launched at ITMA 2015 is also coming up in the
Pakistani market. Durst, Mimaki, EFI Reggiani are also getting a
share. Kornit has showcased their latest version in Fespa 2018.
The scope of digital printer is very promising as the cost of
heads and ink is likely to reduce appreciably as well as the
technique will improve which will attract the printer to adopt
it as soon as possible. Pakistan market is a bit slow to adopt
this technique as they are printing mostly on cheap substrates,
the only local market is supporting the cost. Market trends show
that sooner or later, it is bound to flood the printing market.
DR. John Frost, SPGPrints, MS Lario, Durst and Vincet